Telescope Mechanical Design

Cosmic RAy Telescope for the Effects of Radiation

Telescope Mechanical Design

Albert LinThe Aerospace Corporation

Mechanical Engineer(310) 336-1023

[email protected]/28/05


Overview

Design OverviewInstrument RequirementsMechanical RequirementsDesign DetailsNext Steps


Design Overview• Detectors are housed in stiff structure and decoupled

from the interface circuit board• TEP mounts allow for thermal expansion/contraction• Instrument is shielded and electrically isolated at

interface


Overall Dimensions• Weight = 2.32 lbs

Component Weight (lbs)Structure 1.150Circuit Board 0.300Telescope 0.870Total 2.320


Overview



Instrument RequirementsFrom Instrument Requirements Document (IRD) 32-01205

Item Requirement

CRaTER-L2-04 TEP components of 27 mm and 54 mm in length

CRaTER-L3-01 Adjacent pairs of 140 micron and 1000 micron thick Si detectors

CRaTER-L3-02 Aluminum shielding 0.06” thick

CRaTER-L3-03 0.030” thick aluminum on both ends of the telescope

CRaTER-L3-04 Telescope stack: S1, D1, D2, A1, D3, D4, A2, D5, D6, S2

CRaTER-L3-06 Zenith field of view from D1D6 at 35 degrees

CRaTER-L3-07 Nadir field of view from D3D6 at 75 degrees

All requirements incorporated into model


Telescope GeometryAll Requirements Met A-150 TEP of 27 mm and 54 mm in length Pairs of thin (~140 micron) and thick

(~1000 micron) Si detectors used 0.060” nominal aluminum shielding 0.030” thick aluminum on top and bottom

apertures Telescope stack consistent with

requirement 35 degree FOV Zenith 75 degree FOV Nadir


Overview



Mechanical Requirements• From 431-RQMT-000012, Mechanical System Specifications

Requirement Description Levels

2.1.2Net CG limit loads•Superceded by Random Vibration

12 g

2.4.2Sinusoidal Vibration Loads•Superceded by Random Vibration

Frequency: 5-100 HzProtoflight/Qual: 8gAcceptance: 6.4g

2.5Acoustics•Enclosed box without exposed thin surfaces

OASPL Protoflight/Qual: 141.1 dBOASPL Acceptance: 138.1 dB

2.6.1 Random Vibration See next slide

2.7.2 Shock Environment40 g at 100 Hz2665 g at 1165-3000 HzNo self induced shock

3.1.2.1

3.3

Minimum Fundamental Frequency Minimum > 35 HzRecommended > 50 HzWill not provide FEM model > 75 Hz


Random Vibration• Random Vibration will drive most of the analysis• For resonances in the Random Vibration Spec, Miles’ Equation shows 3 sigma

loading on the order of 100-150 g• Assume Q = 15

Random Vibration Spec

0.01

0.1

11 10 100 1000 10000

Frequency (Hz)

Pow

er S

pect

ral D

ensi

ty (g

^2/H

z)

Protoflight/ Qual

Acceptance

Freq (Hz)

Protoflight/ Qual Acceptance

20 0.026 0.01350 0.16 0.08

800 0.16 0.082000 0.026 0.013


Stress Margins• Load levels are superceded by random vibration spec• Factors of Safety used for corresponding material (MEV 5.1)

– Metals: 1.25 Yield, 1.4 Ultimate– Composite: 1.5 Ultimate

• Margin of Safety = (Allowable Stress or Load)/(Applied Stress or Load x FS) – 1

Description MS yield MS ultimate

Bolt Interface Loading +7,291 +14,709

Interface Circuit Board brittle +0.45

Silicon Detector brittle +48.3

All components have positive Margin of Safety


First Fundamental Frequency• First Fundamental Frequency at 2340 Hz


Overview



How to Mount TEP• Limited Material Properties information on A-150 TEP• Need to mount TEP to

– Minimize deformation of TEP during assembly– Allow for thermal contraction– Exert 20 lbs preload to withstand random vibration

Springs exert 20 lbs at hot and cold cases Detectors

TEP Sample

Solution

• Oversized mounting hole to allow for changes in radial dimension

• Spring clamp to hold in TEP with preload at all temperatures


Mounting Details, Purging and Venting• Detectors mounted using #2-56 fasteners• Pigtail connector feeds through hole and plugs

into the Analog board in the E-box• Spacers between each pair of detectors for

venting• No enclosed cavities• Internal purge line from Ebox connects to

telescope purge system (not shown)– Detailed design of purge system pending

Connection


Overview

Design OverviewTelescope RequirementsMechanical RequirementsDesign DetailsNext Steps


Next Steps• Finalize interface between telescope assembly and electronics box• Detail purge design• Complete drawings for fabrication



Backup Slides


CRaTER-L2-04• 4.4.1 Requirement

Break the TEP into two components, of 27 mm and 54 mm in length.


6.1 CRaTER-L3-01Thin and thick detector pairs• 6.1.1 Requirement

The telescope stack will contain adjacent pairs of thin (approximately 140 micron) and thick (approximately 1000 micron) Si detectors. The thick detectors will be used to characterize energy deposition between approximately 200 keV and 100 MeV. The thin detectors will be used to characterize energy deposits between 2 MeV and 1 GeV.

6.2 CRaTER-L3-02 Nominal instrument shielding• 6.2.1 Requirement

The shielding due to mechanical housing the CRaTER telescope outside of the zenith and nadir fields of view shall be no less than 0.06” of aluminum.


6.3 CRaTER-L3-03 Nadir and zenith field of view shielding• 6.3.1 Requirement

The zenith and nadir sides of the telescope shall have no less than 0.03” of aluminum shielding.

6.4 CRaTER-L3-04 Telescope stack• 6.4.1 Requirement

The telescope will consist of a stack of components labeled from the nadir side as zenith shield (S1), the first pair of thin (D1) and thick (D2) detectors, the first TEP absorber (A1), the second pair of thin (D3) and thick (D4) detectors, the second TEP absorber (A2), the third pair of thin (D5) and thick (D6) detectors, and the final nadir shield (S2).


6.6 CRaTER-L3-06 Zenith field of view• 6.6.1 Requirement

The zenith field of view, defined as D1D6 coincident events incident from deep space, will be 35 degrees full width.

6.7 CRaTER-L3-07 Nadir field of view• 6.7.1 Requirement

The nadir field of view, defined as D3D6 coincident events incident from the lunar surface, will be 75 degrees full width.


Bolt Interface Loading

-3.000

0.000

3.000

6.000

9.000

-3.000 0.000 3.000 6.000 9.000

Mechanical Engineering Design, by Shigley

RP-1228 NASA Fastener Design

First fundamental frequency at 2340 Hz, which is off of the random vibe data set

Assume worst-case loading at 2000 Hz

3 sigma load = 105g

A286 CRES Bolts at Interface

Worst Case Bolt

0 lb 18231 lb 4.71 lb

0 lb 9.63 lb1.2 in 7,291

593 lb 14,709 907 lb356 lb

Margin of Safety Ult

Normal Load Worst Case BoltIn-Plane Load X Normal LoadIn-Plane Load Y Shear LoadIn-Plane Load Offset Margin of Safety YieldTensile Yield

Shear YieldTensile Ultimate


Interface Circuit Board Board Resonance• First Mode: 632 Hz• Total nodes: 25225• Total elements: 12901

COSMOSWorks 2005


Detector Board Stress• Using Miles Equation, assume Q = 15, FS = 1.5• 3σ g loading = 146 g• Material = Polyimide-Glass• Max Stress = 3,663 psi• MS ultimate = 24,000 psi / (1.5 * 3* 3,663 psi) - 1 = 0.45


Detector Analysis• Assuming Q = 15• Detector Material = Silicon• Fundamental Frequency = 2130 Hz; 2000 Hz yields 3 sigma load of 105g• Ultimate Margin of Safety = (17,400 psi / (1.4 * 252 psi) – 1 = 48.3


Sensitivity Analysis• Preceding calculations used a nominal Q of 15• This table shows how the 3 sigma g-loads vary with Fundamental Frequency and Q

(g's)1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000

5 85 81 78 75 72 70 68 66 64 62 6110 121 115 110 106 102 99 96 93 90 88 8615 148 141 135 130 125 121 117 114 111 108 10520 170 163 156 150 144 140 135 131 128 124 12125 191 182 174 168 162 156 151 147 143 139 136

Fundamental Frequency (Hz)

Q F

acto

r

Most structures have Q between 10 and 20


Factors of Safety Used

Table 3.1 from 431-RQMT-000012Type of Hardware Yield UltimateTested Flight Structure - Metallic 1.25 1.4Tested Flgiht Structure - Beryllium 1.4 1.6Tested Flight Structure - Composite N/A 1.5Pressure Loaded Structure 1.25 1.5Pressure Lines and Fittings 1.25 4.0Untestest Flight Structure - Metallic Only 2.0 2.6

Design Factor of Safety


Material Properties

1. MIL-HDBK-5J2. Silicon as a Mechanical Material, Proceedings of the IEEE, Vol 70, No. 5, May 1982, pp 420-4573. www.efunda.com

MaterialDensity (lb/in3)

Young's Modulus

(ksi)Tensile

Yield (ksi)

Tensile Ultimate

(ksi)Poisson's

Ratio Where UsedAluminum 6061-T6 0.098 9,900 35 42 0.33 StructureBeryllium Copper TH02 0.298 18,500 160 185 0.27 TEP SpringA286 AMS 5731 0.287 29,100 85 130 0.31 FastenersSingle Crystal Silicon 0.084 27,557 brittle 17.4 0.19 DetectorsPolyimide-Glass 0.065 2,000 brittle 24 - Circuit Board

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Telescope Mechanical Design